The big blue buildings of Ikea have sprouted solar panels and wind turbines; inside, shelves are stocked with LED lighting and recycled cotton. Why? Because as Steve Howard puts it: “Sustainability has gone from a nice-to-do to a must-do.” Howard, the chief sustainability officer at the furniture megastore, talks about his quest to sell eco-friendly materials and practices — both internally and to worldwide customers — and lays a challenge for other global giants.